.demo{width:100%; position:relative}
#disk{width:70%; height:auto;margin:0px auto;display: block;}
.start{width:30%; height:auto; display:block;position:absolute;top:8%; margin-left:35.5%;}
#start_text{width:17%; height:auto; display:block;position:absolute;top:37.5%; margin-left:42%;}